Magnetic switching assembly

ABSTRACT

A magnetic switching assembly is disclosed in which the magnet stroke for operative switching is reduced while maintaining reasonably wide tolerances in the relative positioning of the components thereby to provide faster and more accurate switching at low cost. In a preferred embodiment of the invention an actuating magnet is positioned adjacent a reed switch for movement toward and away from the switch contacts to provide operative switching in both directions. A second permanent magnet is disposed at right angles to the actuating magnet and is effective to deflect the magnetic field associated therewith thereby to provide a steeper magnetic field strength gradient in the direction of the magnet stroke. The magnet stroke is thereby minimized while maintaining the positioning tolerances of the reed switch and magnet at values permitting low cost manufacture. In another embodiment of the invention, the second magnet which serves to deflect the magnetic field of the driving magnet is formed integral with the driving magnet in an L-shaped configuration.

United States Patent 1 Yanagisawa et al.

11 3,733,569 1 May 15, 1973 I54] MAGNETIC SWITCHING ASSEMBLY [75] lnventors: Noboru Yanagisawa; Taneo Murata,

both of Tokyo, Japan [73] Assignee: Alps Electric Co., Tokyo, Japan [22] Filed: Apr. 25, 1972 [2]] Appl. No.: 247,319

[30] Foreign Application Priority Data Primary ExaminerRoy N. Envall, Jr. Attorney- Maxwell James et al.

[ ABSTRACT A magnetic switching assembly is disclosed in which the magnet stroke for operative switching is reduced while maintaining reasonably wide tolerances in the relative positioning of the components thereby to provide faster and more accurate switching at low cost. In a preferred embodiment of the invention an actuating magnet is positioned adjacent a reed switch for movement toward and away from the switch contacts to provide operative switching in both directions. A second permanent magnet is disposed at right angles to the actuating magnet and is effective to deflect the magnetic field associated therewith thereby to provide a steeper magnetic field strength gradient in the direction of the magnet stroke. The magnet stroke is thereby minimized while maintaining the positioning tolerances of the reed switch and magnet at values permitting low cost manufacture.

In another embodiment of the invention, the second magnet which serves to deflect the magnetic field of the driving magnet is formed integral with the driving magnet in an L-shaped configuration.

12 Claims, 14 Drawing Figures PRIOR ART PRIOR ART PATENTED WW 1 5 3 b /1 HA/ L +L-* Z PRIOR ART PRIOR ART PATENTEB RAY I 51973 SHEET 2 OF 2 1 16. 4 FT/6.5B 1 16.56

FIG 75 FIG. 74

FIG. 64

This invention relates to magnetically actuated switches and more particularly to an improved actuating means for a magnetically actuated switch of the pushbutton type.

Magnetic switching devices are used in a variety of applications particularly in the communications and data processing fields where rapid and reliable manually actuatable switching is required. The most commonly utilized switching device in this category is the reed switch which comprises a pair of contacts encapsulated in glass or the like, those contacts being movable into and out of electrical engagement with each other in response to the variation in magnetic field.

In a typical reed switch assembly, a permanent magnet is positioned adjacent the operative switching device and is movable relative thereto,.thereby to vary the magnetic field strength in the vicinity of the switch contacts. Typically, those contacts are resilient and overlappingly disposed within the glass casing in spaced relationship to provide a resiliently biased normally open circuit between the output leads extending from opposite ends of the casing. As the permanent magnet is moved closer to the switch contacts, the magnetic field strength or flux density in the vicinity of those contacts increases and the spaced contacts are magnetically attracted to one another. That magnetic attraction increases in response to the movement of the permanent magnet until it is sufficient to overcome the resilient bias of the contacts whereupon those contacts are drawn into operative physical and electrical engagement to close the circuit between the output switch terminals. Upon movement of the permanent magnet in the opposite direction away from the switch contacts the reverse effect results the magnetic field strength decreases resulting in a loss of magnetic attraction between the contact arms, whereby those contact arms spring back to their normally open positions.

One of the major difficulties involved in the manufacture of switches of this type is the incompatibility of the requirement of operative switching in response to small movements of the driving magnets with the requirement of reasonable tolerances in the dimensions and relative positions of the operative components. The former requirement relates to both space requirements and speed of operation while the latter bears on cost of manufacture.

The major obstacle to the manufacture of a low cost, high speed miniature switch of the type described results from the hysteresis or lag in switching action between the open and closed positions of the contacts. Thus, it has been found that a greater magnetic field strength is required to overcome the normal bias of the resilient contact arms to effect closing of the switch than is required to maintain those contact arms in the closed position. Accordingly, the magnet must be movable relative to the switch contacts by a minimum distance equal to the distance along its magnetic field gradient between the magnetic field strength above which the normally open contacts will close and that magnetic field strength below which the contacts will open. It is of course desirable to minimize that distance thereby to provide faster switching in a minimum of space. However, attempts at reducing this dimension have generally been unsuccessful because they involve reducing the allowable position tolerances below an economically feasible level.

For example, reed switches of the pushbutton type typically utilize a movable bar magnet having opposite magnetic poles at either end. The magnetic field strength gradient lines of the magnet extend outwardly from either pole in an arcuate configuration, the field strength decreasing in a radially outwardly direction. If the reed switch is disposed opposite one pole of the magnet with the magnet movable toward or away from I the switch contacts, a maximum lateral tolerance for alignment is achieved. However, this arrangement involves relative movement of the magnet along its minimum magnetic field strength gradient (the lowest rate of change of field strength) thereby requiring a maximum travel stroke of the magnet to effect operative switching in both directions. In order to reduce that stroke, the magnet may be positioned closer to the reed switch and movable past the reed switch in a direction parallel to a plane through the switch contacts thereby to take advantage of the steeper magnetic field strength gradient in that direction. This arrangement, however, requires the manufacture of parts and positioning thereof to extremely close tolerances to insure that the magnet is close enough to the switch contacts to effect switching yet to insure against contact with the fragile glass casing. The manufacturing cost is accordingly significantly increased.

It is a primary object of the present invention to provide a magnetically actuated switching device which eliminates substantially all of the foregoing drawbacks of prior art devices of this type.

More particularly, it is an object of the present invention to provide a magnetically actuated switching device having a significantly increased speed of operation and reduced space requirement while at the same time having a low cost of manufacture.

It is yet another object of the present invention to provide a reed switch assembly in which the operative magnet stroke for switching is considerably reduced without reducing the required tolerances on the dimensions and relative positions of the operative components.

It is still another object of the present invention to provide a low cost magnetically actuated switching device of the type described having a reduced size and increased speed, accuracy and reliability heretofore attainable.

To the accomplishment of fliese and other objects, the present invention comprises a reed switch assembly including a pair of normally spaced resilient contact arms encased within an elongated housing, said switching device being actuated by the movement of a permanent magnet movably positioned closely adjacent thereto. The permanent magnet comprises an L-shaped magnetic assembly having a first pole on one leg thereof and a second pole on the other leg thereof. That L-shaped magnet assembly is mounted with its inwardly facing operative surface spaced from the reed switch casing and movable in a direction parallel to one of its legs. The magnetic field associated with the other leg of the magnet is effective to provide operative switching of the resilient contact arms between their normally open position and a closed position resulting from the magnetic attraction of those contact arms effected by an increase in the magnetic field strength as the permanent -magnet is moved toward the reed switch. The magnetic field associated with the second leg of the assembly interferes with the magnetic field associated with the operative switching leg of the magnet and deflects it to a flattened condition, thereby to significantly increase the magnetic field strength gradient in the direction of movement toward and away from the reed switch. Accordingly, this arrangement results in a reduced travel stroke required for effective switching while at the same time maintaining a rather wide lateral tolerance for the positioning of the magnet relative to the reed switch.

To the accomplishment of the above and to such other objects as may hereinafter appear, the present invention relates to a magnetic switching assembly as defined in the appended claims and as described in the specification taken together with the accompanying drawings, in which:

FIGS. 1 and 1A are perspective views of two embodimerits of permanent magnets commonly used in prior art reed switches;

FIGS. 2A, 2B and 2C show three embodiments of prior art reed switch assemblies utilizing the permanent magnet of FIG. 1A wherein the permanent magnet is movable in the direction parallel to the plane of the reed switch;

FIG. 3 is an illustration similar to that of FIGS. 2A, 2B and 2C of another prior art reed switch assembly employing the permanent magnet of FIG. 1A wherein the magnet is movable toward and away from the reed switch in a direction perpendicular to its axis.

FIG. 4 is a graphical illustration of the switching operation of a reed switch as a function of magnetic field strength;

FIG. 5A is a schematic illustration of the magnetic field associated with two permanent magnets disposed at right angles to each other;

FIG. 5B is a side elevational view, partly in section, of one embodiment of the present invention employing two permanent magnets disposed at right angles to each other in contiguous relationship;

FIG. 5C is a side elevational view, partly in section, of a second embodiment of the present invention utilizing a pair of permanent magnets having different dimensions;

FIG. 6A is a side elevational view, partly in section, of a third embodiment of the present invention utilizing an integral L-shaped permanent magnet;

FIG. 6B is a perspective view of the permanent magnet used with the embodiment of FIG. 6A;

FIG. 7A is a side elevational view, partly in section, of a fourth embodiment of the present invention utilizing an integral L-shaped permanent magnet; and

FIG. 7B is a perspective view of the permanent magnet used in the embodiment of FIG. 7A.

Before discussing the construction and operation of the present invention, the operation of the conventional prior art reed switch will be described with reference to FIGS. 1-3.

As perhaps best shown in FIG. 2C, the conventional reed switch comprises a pair of electrically conductive contact arms 12 and 14 mounted in slightly spaced overlapping relationship within a housing or capsule 1 I typically made of glass. The overlapped ends of the contact arms 12 and 14 define the operation contact surfaces, the other ends of those arms extending in opposite directions through the opposite ends of the housing 11 to form the operative output terminals T1 and T2 of the switch. The contact arms 12 and 14 are typically made of a resilient metallic material and in absence of external influences are disposed in the slightly spaced or open position illustrated in FIG. 2C, thereby to define an open circuit between the output switch terminals T1 and T2. The switch is closed by causing the contact arms to move towards each other into operative engagement. This is accomplished by the application of a magnetic field of sufficient strength to provide a magnetic attraction between the contact arms sufficient to overcome their natural resiliency which normally maintains them in the spaced or open position.

The switching action of a reed switch as a function of magnetic field strength (i.e. intensity or flux density through the contacts) is illustrated schematically in FIG. 4. As there shown, if the switch is initially open the magnetic field strength (here represented by flux density B) must be increased (as represented by the lower horizontal line 16 moving to the right) to a value B2 in order for the magnetic attraction between the contacts to increase sufficiently to move the contact arms 12 and 14 into engagement. This movement is accomplished substantially instantaneously (as represented by the vertical line 17 moving up). However, if the magnetic field strength is thereafter reduced below the B2 value (as represented by the upper horizontal line 18 moving to the left), the contacts do not resile back to their open position (FIG. 2C) until the flux density is reduced still further to a value Bl (vertical line 19). (This phenomenon is well known and results, at least in part, from the fact that the force of attraction between the contact arms for a given magnetic field strength is greater when the arms are in contact. It therefore requires a greater field strength to move them into contact than to maintain them in contact).

The difference between the magnetic field strengths B1 and B2, represents the minimum variation in flux density which will efiect operative switching in both directions. That variation is produced in a manually actuated reed switch by the reciprocal movement of a permanent magnet.

Referring specifically to FIG. 1A, there is illustrated a permanent bar magnet 10 of the type used to actuate the conventional reed switch comprising an elongated bar of magnetized material (i.e. ferro-magnetic iron) having a north pole N at one end and a south pole S at its other end. Alternatively, a planar four-pole magnet 10A, such as that illustrated in FIG. 1B, may be utilized. For the sake of simplicity, the reed switch assemblies of FIGS. 2 and 3 are illustrated in connection with an actuating magnet of the two-pole bar type as illustrated in FIG. 1A. It will be appreciated, however, that the principles discussed below apply equally to the use of alternate conventional actuating magnets such as that illustrated in FIG. 1B.

As perhaps best illustrated in FIG. 3, the magnetic field strength (flux density) associated with a pennanent magnet varies as a function of the distance from its poles-the flux density decreases in a direction away from the operative pole. For example, in FIG. 3 the variation in magnetic field strength is illustrated by the solid gradient line B2 which represents the connection between all points having a flux density value of B2 and the broken gradient line B1 which represents the connection of all points having a lower flux density value of B1. Accordingly, when the contact arms 12 and 14 are positioned outside of the area bounded by broken gradient line B1, the contacts are open, as illustrated by the solid line position of the switch 11 in FIG. 3. In order to switch from that open position to the closed position of the contacts, the magnet must be moved downwardly in the X direction by a distance sufficient to bring the contact arms within the area bounded by the solid line B2 within which area the flux density is greater than the value E2, the value sufficient to close the switch contacts (see FIG. 4). Conversely, in order to again open the switch contacts, the magnet 10 must be moved upwardly in the Y direction by a distance sufficient to position the contact arms 12 and 14 outside of the area bounded by the broken gradient line B1 which represents the area within which the magnetic flux density is greater than the value B1. Accordingly, when the reed switch 11 is aligned directly beneath the pole of the magnet 10 as illustrated in solid lines in FIG. 3, the distance D between the lines B1 and B2 along the XY axis represents the minimum distance which the magnet 10 must be adapted to move in order to effect operative switching in both directions (the thickness of the contacts and space therebetween is here neglected for the sake of simplicity). However, clearly some latitude in positioning the reed switch in registration with the magnet pole must be affordedQIn the embodiment of FIG. 3, the maximum latitude or tolerance L of positioning of the reed switch relative to the magnet 10 in a direction perpendicular to the XY axis is defined between the vertical broken lines L1 and L2. As illustrated in broken lines, the reed switch may be positioned anywhere within the broken vertical boundary lines L1 and L2 and still be in registration with at least a portion of the magnetic field within the gradient line B2. However, with the indicated tolerance or latitude L it will be apparent that the magnet 10 must be movable by a minimum distance of D In'order to minimize the distance D by which the magnet must be moved to accomplish switching, the magnet may be positioned for movement in a direction parallel to a plane through the axis of the switch. Three such prior art arrangements are illustrated in FIGS. 2A-2C. In FIG. 2A the magnet 10 is disposed with its north and south poles vertically spaced while the reed switch is horizontally disposed closely adjacent the magnet 10. As the magnet is moved downwardly in the X direction the magnetic field within the solid line B2 associated with the north pole encompasses the contact arms 12 and 14, thereby to close same and upon movement in the opposite Y direction those contacts resile to the open position upon crossing the broken gradient line B1. Since the lines B1 and B2 are closer at the point of crossing of the contacts 12 and 14 in this embodiment (the flux density gradient is steeper in this region), the distance D or D defining the required magnet stroke for operative switching (for the precisely aligned and maximum lateral tolerance conditions, respectively) is reduced. However, in this embodiment the maximum lateral tolerance L of positioning the reed switch relative to the magnet in a direction perpendicular to the XY axis is quite small and accordingly the cost of manufacture is prohibitive.

In the embodiment of FIG. 2B, the magnet is disposed with its north and south poles horizontally spaced in a direction parallel to the axis of the reed switch 11. The magnet is again movable vertically in the XY direction past the reed switch and the operation is substantially identical to that illustrated and described with respect to FIG. 2A.

In the embodiment of FIG. 2C, the reed switch 11 and magnet 10 are both disposed vertically and the magnet is movable vertically in the XY direction. Again, the operation is as described above. It should be noted, however, that in the embodiments of FIGS. 2A, 2B and 2C (as opposed to the embodiment of FIG. 3), the reed switch must be positioned much closer to the magnet so that the allowable tolerances are even further reduced in order to prevent the magnet from actually contacting the fragile glass casing of the reed switch. Moreover, in the embodiments of FIGS. 2A and 2C where the magnet is moved in the direction of its north-south axis, the upper end of the magnet stroke must be quite accurately limited in order to prevent inadvertent closing of the switch contacts by the lower or south pole of the magnet.

It will be apparent from the foregoing that a minimum effective magnet stroke cannot be attained without reducing the required tolerances of positioning of the reed switch and magnet to a value which substantially increases cost. Thus, the embodiments of FIGS. 2A-2C provide for faster switching in less space (i.e. shorter magnet strokes) but at substantially increased cost (resulting from the requirement of closer tolerances) while the lower cost of the reed switch assembly of FIG. 3 (resulting from the wider tolerances permitted) is attained at the sacrifice in speed of operation and space requirements (i.e. longer magnet stroke).

The present invention provides a magnetic switching assembly adapted to provide the shorter magnet stroke of the embodiments of FIGS. 2A-2C for faster switching in less space while at the same time maintaining the wide tolerances for positioning the reed switch relative to the permanent magnet which enables the construction of the assembly at low cost.

FIG. 5A is a schematic illustration (in end view) of two permanent bar magnets 20 and 22 disposed at right angles to each other in spaced relationship. When so disposed, the magnetic fields associated with these magnets (at least the portion interiorally of the broken line B1) do not interfere with one another. However, it has been found that when those magnets are brought into contiguous relationship along one edge as illustrated in the embodiment of FIG. 58, that the fields associated with those magnet poles interact and tend to deflect the field of one magnet away from the magnetized surface of the other magnet. In this embodiment the reed switch 11 is positioned below the south pole of the horizontally disposed actuating magnet 20, that magnet being movable vertically along the XY axis toward and away from the reed switch 11. It will be apparent that the deflection of the magnetic field, represented by the field strength gradient lines B1 and B2, away from the north pole of the vertically disposed magnet 22 results in a flattening of those gradient lines or in other words an increase in the steepness of the magnetic field strength gradient in the direction along the XY axis. Accordingly, the minimum distance D which the magnet 20 must be moved along the XY axis in order to effect operative switching in both directions is substantially reduced as compared to that of the embodiment of FIG. 3. However, it will also be apparent that this reduction in magnet stroke is achieved without any significant decrease in the required lateral tolerance L for the lateral positioning of the reed switch.

Thus the maximum lateral tolerance L within which the reed switch may be positioned and still be in registration with at least a portion of the magnetic field within the gradient line B2 is considerably larger than that of the embodiments of FIGS. 2A-2C. The required magnet stroke D,, for this rather large lateral tolerance L is still considerably smaller than that of the embodiment of FIG. 3. Accordingly, by providing a magnet assembly comprising two bar magnets disposed at right angles and mounted in a suitable framework (not shown) for movement toward and away from the reed switch as illustrated in FIG. B, the advantages of the prior art structures of both FIGS. 2A-2C and FIG. 3 are achieved.

A further modification is illustrated in FIG. 5C. As there shown, the vertically disposed or biasing magnet 22' is considerably smaller than the actuating magnet and accordingly the reed switch 11 may be positioned closer to that biasing magnet thereby reducing the lateral dimension of the switch. Of course, this savings in lateral space is accomplished at some sacrifice in the extent to which the magnet stroke may be minimized since the smaller the biasing magnet, the smaller the deflection of the field associated with the driving magnet and the larger the distance between the gradient lines B1 and B2 in the direction of the XY axis.

In the embodiments of FIGS. 6 and 7, a single integral L-shaped magnet having appropriately positioned poles is substituted for the two magnet assemblies of FIGS. 58 and 5C. The magnet 24 in the embodiment of FIG. 6 is generally equivalent in operation to the two-magnet assembly of FIG. 5B whereas the design of the magnet 26 of the embodiment of FIG. 7 is similar to that of the assembly of FIG. 5C. The use of an integral one-piece magnet eliminates the need for a mounting frame to maintain the magnets of FIGS. 58 and SC in operative relative positions and accordingly substantially reduces the cost of manufacture and assembly. It will be appreciated that the embodiments of FIGS. 5B, 5C, 6 and 7 all provide an improved reed switch assembly which may be assembled at reasonable cost while at the same time providing a substantially increased speed and reliability of operation while minimizing space requirements.

While only a limited number of embodiments of the present invention have been herein specifically described, it will be appreciated that many variations may be made therein without departing from the scope of the invention, as defined in the following claims.

We claim:

1. In a magnetic switching assembly comprising switching means movable between at least two operative switch positions under the influence of a magnetic field, said switching means being movable from a first to a second position upon entering a magnetic field having an intensity greater than a first value and being movable from said second position back to said first position upon moving into a magnetic field having a second intensity less than a second value, said first intensity value being greater than said second intensity value, first permanent magnet means disposed adjacent common plane with said switching means in a first direction toward and away from same, said first magnet means having a normal magnetic field intensity which decreases from a value greater than said first intensity value to a value less than said second intensity value in said first direction, whereby said switching means may be operatively switched between said first and second operative switch positions by a reciprocating movement of said permanent magnet toward and away from said switch means in said first direction by a given minimum distance, the improvement comprising second permanent magnet means adjacent said first permanent magnet means and having a magnetic field extending in a second direction angularly disposed to said first direction, said second magnetic field interfering with said first magnetic field to increase the rate of intensity variation in said first direction thereby to decrease said minimum distance which said first magnet must be moved to effect switching of said switching means between said first and second switch positions.

2. The magnetic switching assembly of claim 1, wherein said first and second permanent magnet means are discrete permanent magnets.

3. The magnetic switching assembly of claim 2, wherein said switching means is a reed switch and wherein said first and second discrete permanent magnets are angularly disposed bar magnets extending in a direction parallel to said reed switch.

4. The magnetic switching assembly of claim 1, wherein said first and second magnet means comprises the angularly disposed legs of a single integral permanent magnet.

5. The magnetic switching assembly of claim 4, wherein said switching means comprises a reed switch and wherein said legs of said permanent magnet lie in planes parallel to the axis of said reed switch.

6. The magnetic switching assembly of claim 4, wherein said first and second magnet means are disposed at right angles to each other.

7. The magnetic switching assembly of claim 6, wherein said first and second permanent magnet means are discrete permanent magnets.

8. The magnetic switching assembly of claim 6, wherein said first and second magnet means comprises the angularly disposed legs of a single integral permanent magnet.

9. The magnetic switching assembly of claim 2, wherein said first and second discrete magnets are of the same size and shape.

10. The magnetic switching assembly of claim 2, wherein said first and second discrete magnets are of different size and shape.

11. The magnetic switching assembly of claim 4, wherein said first and second legs of said integral magnet are of the same size and shape.

12. The magnetic switching assembly of claim 4, wherein said first and second legs of said integral magnet are of different size and shape. 

1. In a magnetic switching assembly comprising switching means movable between at least two operative switch positions under the influence of a magnetic field, said switching means being movable from a first to a second position upon entering a magnetic field having an intensity greater than a first value and being movable from said second position back to said first position upon moving into a magnetic field having a second intensity less than a second value, said first intensity value being greater than said second intensity value, first permanent magnet means disposed adjacent said switching means and reciprocally movable in a common plane with said switching means in a first direction toward and away from same, said first magnet means having a normal magnetic field intensity which decreases from a value greater than said first intensity value to a value less than said second intensity value in said first direction, whereby said switching means may be operatively switched between said first and second operative switch positions by a reciprocating movement of said permanent magnet toward and away from said switch means in said first direction by a given minimum distance, the improvement comprising second permanent magnet means adjacent said first permanent magnet means and having a magnetic field extending in a second direction angularly disposed to said first direction, said second magnetic field interfering with said first magnetic field to increase the rate of intensity variation in said first direction thereby to decrease said minimum distance which said first magnet must be moved to effect switching of said switching means between said first and second switch positions.
 2. The magnetic switching assembly of claim 1, wherein said first and second permanent magnet means are discrete permanent magnets.
 3. The magnetic switching assembly of claim 2, wherein said switching means is a reed switch and wherein said first and second discrete permanent magnets are angularly disposed bar magnets extending in a direction parallel to said reed switch.
 4. The magnetic switching assembly of claim 1, wherein said first and second magnet means comprises the angularly disposed legs of a single integral permanent magnet.
 5. The magnetic switching assembly of claim 4, wherein said switching means comprises a reed switch and wherein said legs of said permanent magnet lie in planes parallel to the axis of said reed switch.
 6. The magnetic switching assembly of claim 4, wherein said first and second magnet means are disposed at right angles to each other.
 7. The magnetic switching assembly of claim 6, wherein said first and second permanent magnet means are discrete permanent magnets.
 8. The magnetic switching assembly of claim 6, wherein said first and second magnet means comprises the angularly disposed legs of a single integral permanent magnet.
 9. The magnetic switching assembly of claim 2, wherein said first and second discrete magnets are of the same size and shape.
 10. The magnetic switching assembly of claim 2, wherein said first and second discrete magnets are of different size and shape.
 11. The magnetic switching assembly of claim 4, wherein said first and second legs of said integral magnet are of the same size and shape.
 12. The magnetic switching assembly of claim 4, wherein said first and second legs of said integral magnet are of different size and shape. 